1. Field of the Invention
The present invention is directed to a method and apparatus for handling tar sands and extracting bitumen or oil from tar sands in an economical and efficient continuous closed loop system.
2. Prior Art
Tar sands, sometimes known as oil sands or bituminous sands, are a combination of clay, sand, water and bitumen. Bitumen is a semisolid form of oil. It is known to mine tar sands to extract the bitumen, which is upgraded into synthetic crude or refined directly into petroleum products.
Tar sands deposits are found in over 70 countries throughout the world and represent as much as two-thirds of the world's reserves of oil.
In the processing of tar sands which contain oil-bearing bitumen, the oil-bearing sands must first be mined, the tar sand must be processed to recover the hydrocarbons and the sand must be cleaned sufficiently to alleviate environmental concerns upon disposal or proper placement back into the environment.
There are various known methods of extracting the bitumen or oil from the tar sands. In one known process, the tar sands are mined and hot water and caustic soda (NaOH) are added to the sand. The resulting slurry is piped to an extraction plant where it is agitated and the oil skimmed from the top.
In an alternate known cold flow process, oil is pumped out of the sands using progressive cavity pumps which lift oil along with sand. This process only works well where the oil or bitumen is fluid enough to pump. Additionally, the sand causes the pumps and other equipment to wear.
In a further alternate known cyclic steam stimulation process, a well is put through cycles of steam injection, soaking, and oil production. Oil or bitumen is thereby extracted. Haefele et al. (U.S. Pat. No. 5,998,640) discloses a solvent extraction method that utilizes pressure to assist in the extraction. By providing a pressure differential, oil free solids may be removed from an oil extraction chamber.
Rosenbloom (U.S. Pat. No. 5,534,136) discloses a tar sand oil extraction system with an initial receptacle 16 which delivers slurry to a separator 20. Occluded oil is then washed with solvent in a screw conveyor. The washed sand is introduced to a solvent recovery furnace to vaporize the solvent.
A large portion of the expense of tar sand processing is in materials handling. The material is sticky, and tough. Conveyors, augers, and crushers wear quickly when handling tar sand. Solvent extraction processes are usually considered to be energy intensive and solvent loss is often an issue. The extraction efficiencies are normally no greater than 85%. In addition, cold weather can shut down most operations.
In order for the extraction of tar sands to be an economical endeavor, the separation process should ideally require low energy, provide a simple material handling method, and recycle most of the chemicals added for processing.
The present invention addresses these issues and also addresses issues concerning energy recycling and solids handling.
Accordingly, it is a principal object and purpose of the present invention to provide a tar sands processing system that does not require high pressure vessels.
It is a further principal object and purpose of the present invention to utilize tar sands as a source of cooling for a solvent condenser.
It is a further object and purpose of the present invention to use an oil/solvent mixture to dissolve, transport and classify the tar sands.
It is a further object and purpose of the present invention to provide a tar sands processing system that recycles most of the solvent used in extraction.
It is a further object and purpose of the present invention to provide a continuous tar sands handling and extraction process at atmospheric pressure in a closed loop system.